Amoeba

Photo by: Steve Young

An amoeba (pronounced uh-MEE-buh) is any of several tiny, one-celled
protozoa in the phylum (or primary division of the animal kingdom)
Sarcodina. Amoebas live in freshwater and salt water, in soil, and as
parasites in moist body parts of animals. They are composed of cytoplasm
(cellular fluid) divided into two parts: a thin, clear, gel-like outer
layer that acts as a membrane (ectoplasm); and an inner, more watery
grainy
mass (endoplasm) containing structures called organelles. Amoebas may
have one or more nuclei, depending upon the species.

The word amoeba comes from a Greek word meaning "to change."
The amoeba moves by continually changing its body shape, forming
extensions called pseudopods (false feet) into which its body then flows.
The pseudopods also are used to surround and capture food—mainly
bacteria, algae, and other protozoa—from the surrounding water. An
opening in the membrane allows the food particles, along with drops of
water, to enter the cell, where they are enclosed in bubblelike chambers
called food vacuoles. There the food is digested by enzymes and absorbed
into the cell. The food vacuoles then disappear. Liquid wastes are
expelled through the membrane.

Water from the surrounding environment flows through the amoeba's
ectoplasm by a process called osmosis. When too much water accumulates in
the cell, the excess is enclosed in a structure called a contractile
vacuole and squirted back out through the cell membrane. The membrane also
allows oxygen to pass into the cell and carbon dioxide to pass out.

The amoeba usually reproduces asexually by a process called binary fission
(splitting in two), in which the cytoplasm simply pinches in half

Amoeba proteus. (Reproduced by permission of

Photo Researchers, Inc.

)

and pulls apart to form two identical organisms (daughter cells). This
occurs after the parent amoeba's genetic (hereditary) material,
contained in the nucleus, is replicated and the nucleus divides (a process
known as mitosis). Thus, the hereditary material is identical in the two
daughter cells. If an amoeba is cut in two, the half that contains the
nucleus can survive and form new cytoplasm. The half without a nucleus
soon dies. This demonstrates the importance of the nucleus in
reproduction.

Some amoebas protect their bodies by covering themselves with sand grains.
Others secrete a hardened shell that forms around them that has a
mouthlike opening through which they extend their pseudopods. Certain
relatives of the amoeba have whiplike organs of locomotion called flagella
instead of pseudopods. When water or food is scarce, some amoebas respond
by rolling into a ball and secreting a protective body covering called a
cyst membrane. They exist in cyst form until conditions are more favorable
for survival outside.

Words to Know

Asexual reproduction:
Any reproductive process that does not involve the union of two
individuals in the exchange of genetic material.

Cytoplasm:
The semifluid substance of a cell containing organelles and enclosed by
the cell membrane.

Organelle:
A functional structure within the cytoplasm of a cell, usually enclosed
by its own membrane.

Osmosis:
The movement of water across a semipermeable membrane from an area of
its greater concentration to an area of its lesser concentration.

Protozoan:
A single-celled, animal-like organism.

Pseudopod:
From pseudo, meaning "false," and pod, meaning
"foot"; a temporary extension from a cell used in movement
and food capture.

Some common species of amoebas feed on decaying matter at the bottom of
freshwater streams and stagnant ponds. The best-known of these,
Amoeba proteus,
is used for teaching and cell biology research. Parasitic species include
Entamoeba coli,
which resides harmlessly in human intestines, and
Entamoeba histolytica,
which is found in places where sanitation is poor and is carried by
polluted water and sewage. Infection
with
Entamoeba histolytica
causes a serious intestinal disease called amoebic dysentery, marked by
severe diarrhea, fever, and dehydration.

I saw a disfigured pic of a white males head under the title amoeba protoza, is this some type of rare condition? if so could someone point me in the right direction to learn more about this?
thank you...tom

it is nice to read such an incredable point about amoeba.but I have a question,about bacteria,that is amoeba agravate or getting worth when a person has an amoeba cist eats some types of food like vegitables,milk and milk products,fruits ..etc?

Just learning that my Husbnd has an Amoeba in his intestines.He hasnt been out of the Country.His stomach problems have kept him home for a number of years.Any Idea as to how this could have been contacted.I did wonder if his having quite a few Colonascopy;s in a very busy office if this could be the cause.

Thank you for this informative article, never too old to learn, that's for sure. Can you please tell me more about the amoeba parasite, what symptoms it causes, what the effect on the body and specific organs and one's overall wellbeing can be, how do you get rid of it

I really enjoyed this piece on amoeba's it has gave me a lot of good detail for my amoeba poster and has really helped this piece has nice pictures and very good wording nice job i give this piece 5 stars :)

Hi, I have a soil sample that caused my dog to contract canine dysautonomia, which I believe is related to ameboa. I believe that commercial potting soil companies are using water sludge from the southern state areas in their products. If any students or anybody interested I can send you a soil sample for testing. Thank you, Carly
York. Carly1@gmail.com

This was a great resource for my science project and I will probably use it for projects later on. I am sure to get an A on my project and thx for all of the info I need and all correct facts
thx again,
Anymous

I've been searching for this all morning , the question is , " Where in the amoebas cell do most of the chemical reactions happen ? " and my question number 2 is , " The cell membrane of the amoeba has 2 jobs , What are they ? " thank you , they are my questions I hope somebody gets back to me asap because its for homework for tomorrow ! thanks , kind regards Catherine Chapman .

After crashing a a knee board in a warm fresh water lake I very quickly got a severe sinus infection, was given antibiotics but once they were gone I got sicker, had viral meningitis and with in two days had h flu bacterial meningitis. Yes, I survived but with several psychological and emotional side effects that STRANGELY change from apt to apt. No one psychiatrist can give me a "true" dx. Could the ameba have survived in me? Seizures also present at times sometimes I see things but nothing sticks, so could it still b in me?